The single ring arylamines o-toluidine, o-anisidine, m-cresidine (4-methoxy-2-methyl-aniline) and p-cresidine (2-methoxy-tmethylaniline) have recently been found to be active in producing a variety of cancers, including urinary bladder cancer, in rodents. All of these carcinogens have in common the structural feature of a methyl or a methoxy group ortho to the amine. The significance of this feature is apparent in view of the fact that m- and p-toluidines and m- and p-anisidines were found to be inactive or, at the most, only marginally active as carcinogens. Similar enhancement or modulation of carcinogenicity due to o-methyl substitution has also been observed with other arylamines. In previous work, we have synthesized 14C-labeled o-toluidine and studied its metabolism in F-344 rats. To clarify the mechanism of the peculiar ortho methyl/methoxy effect, we now propose to synthesize 14C-labeled m- and p-toluidines; the 14C-labeled o-, m- and p-anisidines and also m- and p-cresidines. Comprehensive comparative in vivo and in vitro studies will then be performed to compare the metabolic pathways of activation and detoxication of these isomers and to correlate these with their known carcinogenicity. From the leads obtained from such metabolism studies, likely proximate forms of the carcinogens will be prepared and their mutagenicity and reactivity in model systems will be compared. Finally, from such screening procedures, the most likely proximate forms will be tested in animal bioassays. Since most of the single ring arylamines in this program are important intermediates in the manufacture of dyes, human exposure to these agents may not be unlikely. It is hoped that the information as to mechanism of these agents gained from this program may provide leads to rational preventive measures.